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York Affinity Heat Pump Demand Defrost

I have a York heat pump system and I believe my demand defrost is not working properly. When the defrost cycle is working, the air out of the registers in my house drops to around 50F. The defrost cycle runs about 7 minutes and never seems to quite remove all the ice/frost on the outside unit. I am concerned that it will not be a sufficient defrost when the temperature is really low and there is ice and snow.
My system is:
York Affinity 18 SEER YZH04811 heat pump
York modular air handler MV20DN21
15KW strip heater
Honeywell TH8320 thermostat
When the heating is working, the temperature out of my registers is between 90F and 95F.
The demand defrost board has been replaced in the last two months when we first complained that the defrost cycle did not fully remove all ice/frost or snow. After replacement the service tech forced the defrost cycle. The outside unit heated up and warm air came out of the inside registers (had a smell like the heating element had not been on for a long time- like burning dust). Now when the defrost comes on normally, as I wrote before, the temperature out of the registers is about 50F.
I suspect a wiring error at the install (over three years ago). Or a loose wire/connection. Could a jumper on the demand defrost or air handler circuit boards be wrong?
Or is it proper for 50F air to come out when the defrost is on?
Any help is appreciated.

If he forced it and it worked, then wiring is PROBABLY correct and the equipment seems to function as it should.

I might look at programming, for the 50° air.

As for the defrost not getting all the ice off, may or may not be correctable issue. It could be anything from incorrect charge to incorrect placement of sensors.

The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
from an excerpt by Paul Jacob in Sun City, AZ

It may be the jumper setting on the defrost board. Forcing defrost will not give the same results as an equipment controlled defrost. Do you know which setting this jumper is currently on? Also have you tech check the numbers on the processor of the board with York. There were some boards with certain #s that had defrost issues. There is also a change in the wiring in the air handler that will control how much strip heat is activated during defrost, have them check that as well.

Jumpers on York boards

I think I have attached photos I took when the technician had the outside unit cover off and the air handler cover off. Perhaps you can see how the jumpers are set. The BP is 35, the LTCO is maybe zero. The defrost curve is set for 2. I do not know what the other jumpers do.
One of my concerns is whether there is a qualified York dealer in my area to service this system. The one who installed it is now out of business.
The guy who swapped the demand defrost board said he had never seen one before. He is willing to come out and try different jumper settings, but that sounds haphazard to me.
Thanks again for your thoughts.

could you get a closer shot of the indoor board with the terminal letters showing and wires going to them; IE R,W,G, etc?

The qualifications should be York dealer first, but if none than a qualified tech is just as good. Just because they are no affiliated with the equipment does not mean they will not do a quality job.

The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
from an excerpt by Paul Jacob in Sun City, AZ

If the number on the sticker in the upper left of the first pic is 109 (it's upside down) then you have the updated board and it should be ok. Any decent tech should be able to take the manual for the indoor unit and determine how the defrost auxiliary heat is configured. Have him make sure the compressor delay jumper on the outdoor board is set to ON, and have him change the defrost curve jumper to 5. This will give quieter shifting in defrost and a longer defrost cycle.

More questions on York air handler

I have been looking at the jumpers on the air handler board. The customer booklet that came with my units has several tables to describe how to set the Cool, Adjust and Heat jumpers. My jumpers are set for Heat-C, Cool-D and Adjust-A. My air handler is a 20D model. The instructions say to consult the Tabular Sheet for the outdoor unit for what CFM. The Tabular sheet says the CFM for a YZH04811 is 3376 CFM. That value does not appear in any of the entries in the table in the air handler manual(range is 1334 to 2209). Am I totally off base trying to figure this out?
Also, the Delay jumper is set for Normal. Would Temperate make more sense? Or does it matter?
Thanks for the help so far. I want to be as knowledgeable as possible when we get the service tech out here.

You must be reading something wrong. For a 4 ton unit you should be around 1600 cfm. Like beenthere said the airflow settings won't affect the defrost operation or length. Get the tech out there and let him do his thing. A simple wiring change in the AHU and a jumper change should solve your problems. I did the same thing for one of our customers with the same problem not long ago and they're happy campers now.

Final question

Thanks for all the suggestions thus far. But before I call a York dealer, can someone definitively tell me if it is wrong for 50F temperature air to be coming out of my registers in the house when a defrost is happening on the outside unit?
When the defrost cycle ends, a heating cycle usually starts and all runs okay then- temp coming out is in the 90s.

The 50 degree air temp into your home is the AC in the defrost cycle and would be right. However, that temp suggests your strip/backup heat is not energizing to temper the air to a higher acceptable supply temperature.

Yes, your defrost function and backup heat along with the complete system should be checked by an experienced HP pro